The present invention relates to an electrophotography, and more particularly to an electrophotographic apparatus which can form or print any desired number of duplicated copies for each of a plurality of documents or manuscripts in a speedy and simple manner.
In the electrophotographic apparatus it is necessary to control accurately various operations such as feeding of a record paper, movement of photosensitive member, e.g. a rotation of a photosensitive drum, operations of a developing device, a uniformly charging device, a cleaning device, etc., in accordance with an exposure-scanning of a document. In order to effect such a control there have been proposed various systems. Heretofore almost all electrophotographic apparatuses can form a single copy by means of a single exposure of the document to be duplicated, and thus have a single sequence of operation control. Therefore the control of such electrophotographic apparatus is rather simple and easy. In a typical construction as a basis for the control use is made of a rotation angle of a photosensitive drum on which an electrostatic charge latent image is formed. That is to say there are provided a plurality of switches which are actuated by one or more cams in accordance with the rotation angle of the drum and various parts of the apparatus are controlled by these switches. However in such an apparatus using a number of mechanical switches adjustment of the apparatus is quite combersome and time consuming work and further it is rather difficult to obtain a space for arranging the switches. Moreover the mechanical switches have relatively short life time due to wear. In order to avoid such disadvantages it has been also proposed to control the various sections by producing clock pulses in accordance with the movement of the basic member such as the photosensitive drum. The clock pulses are counted to produce a timing pulse each time the drum rotates by a predetermined angle, for instance one degree and the timing pulses are counted to produce various control pulses in synchronism with the rotation angle of the drum. For example, such a control system has been disclosed in a U.S. Pat. No. 3,510,125, Japanese Patent Application Laid-Open Publication No. 9,252/74, No. 11,443/75 and No. 21,085/76. Such a system may be classified into two groups, in a first group the generation of timing pulses is initiated at a predetermined standard point on the drum, and in a second group the generation of timing pulses is started at any point on the drum. If the drum has a seam or joint it is inherent to adopt the control system belonging to the first group, because otherwise there is formed a line or seam in the latent image and thus in a final duplicated copy. On the contrary in case of using a drum of seamless type it is possible to initiate the generation of the timing pulses at any point on the drum. In other words it is possible to form the latent image on any position of the drum. In the above mentioned Japanese Patent Application Laid-Open Publication No. 9,252/74 and No. 11,443/75 it is not disclosed from which point on the drum the counting of clock pulses should be started. In the Japanese Patent Application Laid-Open Publication No. 21,085/76 it is described that the counting is initiated at a given standard point on the drum.
In another type of an electrophotographic apparatus any number of duplicated copies can be printed by, for instance, successively repeating development and transferring steps for the same and single latent image which has been once formed on the photosensitive member by a single exposure-scanning of the document. In such an apparatus since successive steps for forming a first copy are different from those for printing other copies and thus the control might be extremely complicated.
In the known timing pulse control system since there is provided only single timing pulse generating means when successive duplicating operations should be effected, it is necessary to initiate a next sequential control after a first controlling sequence has been completely finished. Therefore there is always existent a certain waiting time and thus the duplicating operation could not be controlled in an efficient manner. For instance, in case of forming a plurality of copies for each of a plurality of documents it is advantageous that an interval between a duplicating operation for one document and that for a next document is made short. To this end it is preferable to start the duplicating operation for the next document before the duplicating operation for the first document has been completely finished. It has been found to be quite difficult to control the duplicating operation in a manner just mentioned above by means of the timing pulse control system comprising the single timing pulse generator. Particularly, in the multiple copying apparatus for forming a plurality of duplicated copies by the single exposure-scanning the construction of a control section such as the timing pulse generator, control signal generator, etc. becomes extremely complicated.